1. Field
Embodiments of the invention relate to the field of electrical connectors, and more specifically, to add-in card to backplane connectors.
2. Background
Driven by increasing bandwidth demands, computer bus speeds continue to increase. Currently, numerous buses operate at multiple Gigabits per second. These multiple Gigabit buses demand relatively high connector performance. In particular, as bus speeds increase, relatively high connector cross-talk performance becomes increasingly difficult to achieve at relatively reasonable costs. For example, it is typically difficult to achieve 1–3% crosstalk at multiple Gigabit frequencies, while keeping productions costs to a relatively reasonable level.
Currently, relatively high performance backplane connectors achieve relatively low cross-talk using ground planes and ground pins to isolate electromagnetic fields. For example, pin-and-socket type backplane connectors employ both internal ground planes and ground pins. Beam-and-blade board-to-board type connectors also employ internal ground planes to reduce crosstalk. However, these internal ground plane connectors are not suitable for use in desktop computers because of their relatively high cost and unsuitable form factor.
Another prior art connector type uses multi-level contacts for reducing crosstalk. FIG. 1 illustrates a prior art socket for receiving prior art add-in cards. In FIG. 1, the socket 100 includes a housing 102. Inside the housing 102, the socket includes a first row of low-level ground contacts 104 for grounding an add-in card. The socket also includes a second row of high-level signal and ground contacts 106. In the second row of contacts, at certain intervals, the high-level signal contacts are separated by high-level ground contacts to reduce crosstalk between the signal contacts.
FIG. 2 illustrates a prior art add-in card. In FIG. 2, a prior art add-in card 200 includes two sets of edge fingers 202. Each set of edge fingers 202 includes a row of low-level ground contacts 204, which make contact with the socket's low-level ground contacts 104, when the add-in card 200 is plugged into the socket 100. Each edge finger set also includes a row of high-level signal and ground contacts 206, which mate (i.e., make contact with) with the socket's high-level signal and ground contacts 106, when the add-in card 200 is plugged into the socket 100.
As shown in FIG. 1, one disadvantage of the prior art socket 100 is that its adjacent signal contacts are not always uniform. As such, delay errors can be introduced into signals passing through the signal contacts 106. Another disadvantage of the prior art socket is that the low-level ground contacts 104 do not provide effective crosstalk protection at high bus speeds.